This invention relates to a tire valve suitable for detecting the pressure or temperature in the tire, the strain of the tire wheel and the like.
Concerning an example of conventional devices for detecting the tire pressure, known are devices in which the detective means are fitted on the tire side, and, by applying electromagnetic induction, resonance of electromagnetic waves, etc., the tire pressure can be detected even while the automobile is in operation. They are called the non-contact system. Besides, other devices which trasmit the tire pressure through a slip ring, bar-type tire gauge, etc., the so-called contact system, are also known.
The tire pressure detective devices of the non-contact system among them have disadvantages that they are intricate in mechanism and expensive in manufacturing cost, and that the wheels are especially made for this system, the modification and the like of autombiles to use the system being are required. Further, it is difficult and costly to manufacture these devices so that they are durable in the face of environmental changes and are reliable and of consistent quality.
On the other hand, the tire pressure detective devices of the contact system have hitherto been developed as a low-cost means. However, when they break down, the air in the tire is released to the atmosphere due to their original construction. And defective operation, etc. are apt to occur under low temperature, due to freezing, during the winter season. Therefore, they have problems in reliability and safety, so they have not yet attained the stage practical use. Moreover, regardless of the tire pressure detective device, the tire valves are merely manufactured for the purpose of smoothly getting air into the tire while staying airtight, so they have a shortcoming that they have not the structure meeting the purpose of detecting the pressure, temperature, etc. in the tire.
Furthermore, for example, such a tire pressure indicator as described in an invention disclosed in U.S. Pat. No. 4,308,520 is known: a switch assembly, into which a suitable gas such as dry nitrogen is introduced, is mounted in a wheel-mounted transponder unit. The tire pressure is detected by this assembly. And the transponder unit induces a signal of a phase polarity corresponding to whether the tire pressure is "safe" or "low", which signal is processed by a separate handheld interrogator unit indicates whether the tire pressure is "safe" or "low".
However, the tire pressure indicator has drawbacks that the switch assembly is forced to be constructed unavoidably large; besides, as lead connecting the switch assembly with coil and terminals, etc. for connecting the lead are provided in the transponder unit, the unit is also obliged to become large size.
An invention related to the present invention is disclosed in U.S. Pat No. 4,918,423, having an assignee in common with one of the present assignees.